Photographic processes

ABSTRACT

A UNIFORM BLUE LIGHT EXPOSURE OF PHOTOGRAPHIC SILVER HALIDE GRAINS HAVING CERTAIN SPECTRAL SENSITIZING DYES ADSORBED THERETO, WHILE THE GRAINS ARE MAINTAINED AT TEMPERATURES BELOW ABOUT -180*C., FOLLOWED BY WARMING TO AMBIENT TEMPERATURES, INCREASES THE SPEED AND CONTRAST OF THE SILVER HALIDE GRAINS DURING SUBSEQUENT IMAGE EXPOSURE.

Aug. 1, 1972 M. KELLOGG PHOTOGRAPHICI PROCESSES Filed April 21, 1971 I DE/VS/TY 2.0

2 Sheets-Sheet l INVENTOK ATTORNEY Aug. 1, 1972 1.. M. KELLOGG PHOTOGRAPHIC PROCESSES 2 Sheets-Sheet 2 Filed April '2 1971 INVENTOR.

x k \WEMQ ATTORNEY United States Patent 3,681,077 PHOTOGRAPHIC PROCESSES Lillian M. Kellogg, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N. Filed Apr. 21, 1971, Ser. No. 136,001 Int. Cl. G030 1/28, 5/32 US. Cl. 96-107 19 Claims ABSTRACT OF THE DISCLOSURE This invention relates to photographic processes and products and more particularly to photographic processes and products in which silver halide emulsions are exposed at low temperatures.

West in Photographic Science and Engineering, vol. 6, No. 2, p. 92 (1962) at p. 95 observes that the absorption of visible light by silver halide decreases with decreasing temperatures. In addition, there is exhibited with decreasing temperatures a corresponding decrease in the region of inherent absorption over which the silver halide absorbs. As shown by West, the presence of spectral sensitizing dyes in the emulsion tends to further decrease the sensitivity of the silver halide at low temperature exposure.

James, in US. patent application 822,670 filed May 7, 1969, and in Photographic Science and Engineering, vol. 14, No. 1, J anuary-February 1971, pp. 8486, teaches that the sensitivity and contrast of photographic silver halide emulsions to be exposed at low temperatures (i.e., below about 180 C.) can be increased by adsorbing certain methine dyes to the silver halide grains. The useful methine dyes are described as those in which the highest occupied electronic energy level of the dye, in its unaggregated form at room temperature, is more positive than the highest occupied energy level in the valence band of the silver halide, and the lowest vacant electronic energy level of the dye, in its unaggregated form at room temperature, is more positive than the conduction band of the silver halide. The dyes are employed in rather large concentrations with best results being obtained when the grains have a monolayer coverage of the dye. It would be desirable to make still further improvements in the photographic processes and elements described by James.

Accordingly, one aspect of the present invention is directed to photographic processes producing a silver halide emulsion having increased speed and contrast. Another aspect of the present invention is to provide photographic processes which yield silver halide emulsions exhibiting increased speed and contrast during image exposure at temperatures from about 180 C. to temperatures substantially higher, and to products of such processes. Yet another aspect of the present invention is to provide photographic processes for increasing the sensitivity at low temperatures of a silver halide emulsion containing spectral sensitizing dyes. Other aspects of the invention will be apparent from the disclosure herein and the appended claims.

According to one method of the present invention, a process is provided for increasing the speed and contrast of photographic silver halide grains free from chemical foggants and having adsorbed thereto a methine sensitizing dye, the highest occupied electronic energy level of Ice.

said dye, in its unaggregated form at room temperature, being more positive than the highest occupied energy level in the valence band of the silver halide, and the lowest vacant electronic energy level of said dye, in its unaggregrated form at room temperature, being more positive than the conduction band of the silver halide, said dye trapping electrons at a depth of not more than .7 ev. below the conduction band of the silver halide at temperatures below about C., said silver halide having a suflicient amount of said dye adsorbed thereto to efl ectively increase the speed of said silver halide when exposed at a temperature below about 180 C. The improvement of this invention comprises:

(1) cooling the silver halide grains to a temperature below According to another method of the present invention, a photographic process is provided for increasing the speed and contrast in the region of spectral sensitization of light-sensitive photographic silver halide grains having.

adsorbed thereto a methine sensitizing dye of the type described herein, wherein the dyed emulsion is first cooled to a temperature below about 180 C., and then uniformly exposed to radiation having a wavelength of from about 370 to about 460 nm. for suflicient time to produce a latent image having a density at least about 70% of the maximum developable density. The exposure emulsion is thereafter uniformly exposed at a temperature of less than about 180 C. to a Herschel exposure to destroy the latent image produced by the blue light exposure. The emulsion is then warmed to room temperature. This treatment increases the speed and contrast of the emulsion, particularly in the region of spectral sensitivity provided by the dye, for subsequent image exposures at temperatures ranging from below 180 C. up to about 50 C. or higher. Unusually high speeds are achieved when the dyed emulsion so treated is image-exposed at about 180 C. Preferably, the Herschel exposure employs radiation longer than about 620 nm.

The above methods of the present invention differ from the room temperature flash pre-exposure treatments, commonly used in the prior art to increase the speed of emulsions, in the temperature and method of the pre-exposure. Specifically, the pro-exposure is carried out at a temperature of less than about 180 C., using radiation of between about 370 to about 460 nm. The overall, nonimagewise pre-exposure can vary in intensity from amounts sufficient to give maximum developable density down to weak pre-exposures which result in increases in fog up to about 0.2. Although the prior art room temperature flash pre-exposure increases the speed of some undyed emulsions, it does not increase the speed of the dyed emulsion studied here. Also, speed increases of the undyed emulsion flashed at room temperature for subsequent exposure is much less than that observed when the emulsion is given a uniform blue exposure at about 180 C. It is further to be noted that room temperature Herschel exposures do not increase the speed or contrast of the dyed and undyed emulsions studied here no matter what the temperature of the prior blue light exposure.

The practice of the above methods of the present invention results in substantial increases in speed on exposure at low temperatures up to temperatures substantially above 180 C., such as 0 up to 50 C. or higher. In addition, very high contrast can be obtained in the similar to that obtained with lith-type emulsions used with lith-type developers. These results are particularly unexpected since methine dyes in silver halide emulsions gen erally decrease low temperature sensitivity, as shown by West, Photographic Science and Engineering, vol. 6, No. 2, p. 92 (1962) at p. 100. 7

FIGS. 1 through 3 illustrate the characteristic curves of the photographic images made'by low and room temperature exposures in accordance with the present invention, and show comparative characteristic curves for exposures made at low and room temperatures but not employing the processes of the invention. In each figure, density is plotted on the ordinate and relative log exposure on the abscissa. Curves 2, 3 and of FIG. 1, curves 2, 3 and 5 of FIG. 2, and curves 2 and 4 of FIG. 3 show the increased emulsion speed and contrast obtained when carrying out the processes of the invention. Curves 1 and 4 of FIG. 1, curves 1 and 4 of FIG. 2, and curves 1 and 3 of FIG. 3 are characteristic for dyed and undyedemulsions exposed according to methods falling outside the present invention. These curves are further explained in the examples given below.

Any methine dye can be used in the practice of. the invention, provided the highest occupied electronic energy level of the dye adsorbed on the silver halide, in its unaggregated form at room temperature, is more positive than the highest occupied energy level in the valence band of the silver halide, and the lowest vacant electronic energy level of the dye adsorbed on the silver halide, in its unaggregated form at room temperature, is more positive than the conduction band of the silver halide. The highest occupied electronic energy level of methine dyes adsorbed on silver halide is preferably more negative than the conduction band of the silver halide. The highest occupied electronic energy level of a methine dye adsorbed on silver halide, and the lowest vacantelectronic energy level of a methine dye adsorbed on silver halide, can be calculated by the method described by Tani and Kikuchi, Photographic Science and Engineering, vol. 11, No. 3, p. 129 (1967) and Tani, Kikuchi, and Honda in Photographic Science and Engineering, vol. 2, p. 80 (1968).

At temperature below about 180 C., the dyes employed herein trap electrons at a depth of not more than .7 ev., and preferably not more than .4 ev., below the conduction band of the silver halide. These calculations can be made by the, procedure described by Berry in the Journal of Photographic Science, 1970, vol. 18, No. 5, p. 169 at p. 174.

The highest occupied energy level in thevalence band ofsilver halide and the bottom conduction band of the silver halide has been determined by those skilled in the art. See, for example, Mees and James, The Theory of the Photographic Process, 3rd edition (the MacMillian Company, 1966), pp. 19-21, 264 and 2 65, and Tani, Kikuchi and Honda, Photographic Science and Engineer ing, vol. 12, No. 2 (1968), p. 80. The highest occupied energy level of the valence band of silver halide is about 6.0 ev. relative to 0 for vacuum, and the bottom of the conduction band of silver halide is about 3.5 ev. The values which have been calculated for pure silver bromide result in an energy level in the valence band of approximately 6.0 ev. 'relative to 0 for vacuum, with the electronic energy of the bottom of the conduction band of the silver bromide being approximately 3.5 ev. Further description of the mechanism for calculating the highest occupied energy level in the valence band and the invention, provided the dyes meet the criteria given above. Especially good results are obtained with methine dyes which meet the above criteria and have at least one of the following formulas:

In the above formulas, h, m, n and p each represents an integer of from 1 to 2; L represents a methine linkage, e.g., -CR=, -C(CH C(C H etc.; R R and R each represents an alkyl group, including substituted alkyl (preferably a lower alkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, hexyl, cyclohexyl, decyl, dodecyl, etc., and substituted alkyl groups (preferably a substituted lower alkyl containing from 1 to 4 carbon atoms), such as a hydroxyalkyl group, e.g., fl-hydroxyethyl, w-hydroxybutyl, etc., an alkoxyalkyl group, e.g., fi-methoxyethyl, w-butoxybutyl, etc., a carboxyalkyl group, e.g., fi-carboxyethyl, w-carboxbutyl, etc., a sulfoalkyl group, e.g., fl-sulfoethyl, w-sulfobutyl, etc., a sulfatoalkyl group, e.g., fi-sulfatoethyl, w-sulfatobutyl, etc., an acyloxyalkyl group, e.g., B-acetoxyethyl, -acetoxypropyl, w-butyryloxybutyl, etc., an alkoxycarbonylalkyl group, e.g., fl-methoxycarbonylethyl, w-ethoxycarbonylbutyl, etc., or'an aryl group, e.g., phenyl, tolyl, naphthyl, methoxyphenyl, chlorophenyl, etc.; R and R each represents'the same or a different alkyl group containing from 1 to 6 carbon atoms, e.g., methyl, ethyl, isopropyl, butyl, 2-cyanoethyl, hexyl, etc.; X and X each represents any acid anion, such as chloride, perchlorate, sulfonate, p-toluenesulfonate and which may be combined in R or R when the dye is a betaine; Z Z and 2; each represents the non-metallic atoms necessary to complete the same or different 5- to G-mernbered heterocyclic nucleus of the type used in methine dyes, which nucleus may contain a second hetero atom such as oxygen, sulfur, selenium ornitrogen, such as the following nuclei: a thiazole nucleus, e.g., thiazole, 4-methylthiaiole, 4-phenylthiazole, S-methylthiaZole, 5-phenylthiazole, 4,5-dimethylthiazole, 4,5-diphenylthiazole', 4-(2-thienyl)thiazole, benzothiazole, 4-chlorobenzothiazole, 5-chlorobenzothiazole, 6-chlorobenzothiazole, 7-chlorobenzothiazole, 4-methylbenzothi azole, 5-methylbenzothiazole, 6-methylbenzothiazole, 5-

bromobenzothiazole, 6-bromobenzothiazole, 5 -phenylbenzothiazole, 4-methoxybenzothiazole, S-methoxybenzothb azole, 6-methoxybenzothiazole, 5-iodobenzothiazole, 6- iodobenzothiazole, 4-ethoxybenzothiazole, ,S-ethoxyberizothiazole, tetrahydrobenzothiazole, 5,6-dimethoxybenzothiazole, 5,6:dioxyrnethylenebenzothiazole, 5 hydroxybenzothiazole, 6-hydroxybenzothiazole, naphtho[2,1-d]thiazole, naphtho 1,2-d] thiazole, S-methoxynaphtho [2,3-d]- thiazole, 5 ethoxynaphtho[2,3-d]thiazole, 8 methoxynaphtho[2,3-d]thiazole, 7 methoxynaphtho[2,3-d]thiazole, 4 methoxythianaphthenofi',6,4,5-thiazole, etc.; an oxazole nucleus, e.g., 4-methyloxazole, S-methyloxazole, 4-phenyloxazole, 4,5-diphenyloxazole, ,4-ethyloxazole, 4,5-dimethyloxazole, S-phenyloxazole, benzoxa- 4 phenylselenazole, benzoselenazole, 5 chlorobenzoselenazole, S-methoxybenzoselenazole, S-hydroxybenzoselenazole, tetrahydrobenzoselenazole, naphtho[2,l-d]- selenazole, naphtho[l,2-d]selenazole, etc.; and, a quinoline nucleus, e.g., Z-quinoline, 3-methyl-2-quinoline, 5- ethyI-Z-quinoline, 6chloro-2-quinoline, 8-chloro-2-quinoline, 6-methoxy-2-quinoline, 8-ethoxy-2 -quinoline, .8-hydroxy-Z-quinoline, 4-quinoline, 6-methoxy-4-quinoline, v7- methyl-4-quinoline, 8-chloro-4-quinoline, l-isoquinoline, 3,4-dihydro-l-isoquinoline, 3-isoquinoline, etc. Dyes of Formula 1 above wherein h representsl and Z and Z each represents a quinoline nucleus,.i.-e., quinoline monomethine cyanine dyes, provide particularly good results in the practice of this invention. Some specific dyes which can be used in this invention are listed below:

2-(p-dimethylaminostyryl)-l-methyl pyridinium salt l,l'-diethy1-2,2'-cyanine salt 1,1'-dimethyl-2,2'-cyanine salt 1,l'-dimethyl2,4'-cyanine salt l-methyl-1',9-diethyl-2,2'-cyanine salt 1,1,3,3-tetramethyl-2,2'-cyanine salt 3,3'-diethylthiacarbocyanine salt 3,3'-diethyloxacarbocyanine salt 1',3-diethylselena-2'-cyanine salt 1,1-diphenyl-2,4'-cyanine salt Anhyldro-1'-ethyl-3 fi-sulfoethylthia-2'-cyanine hydroxide.

Dyes particularly useful in carrying outthe method of the present invention for increasing the speed and contrast of photographic silver halide grains are l,l'-diethyl- 2,2 cyanine-chloride, 1,1',3,3'-tetramethyl-2,2'cyanine p toluenesulfonate, 3,3 diethyl 9 methylthiacarbocyanine bromide, 3,3'-diethylthiacarbocyanine p-toluenesulfonate, 1,1-diethyl-2,4'-cyanine chloride, and 1,-1'-di-' methyl2,2-'cyanine p-toluenesulfonate.

The useful concentration of the dyes which can be employed in the practice of this invention will be largely dependent upon the type of dye used, the size and type of the silver halide grains employed, and the particular results desired. Generally good results are obtained with about .1 to 1 gram of dye per mole of silver, although higher concentrations can be employed. With some particular dyes, advantageous efifects are obtained with as low as about 10% of monomolecular layer coverage, with effects increasing with increased dye concentrations up to monomolecular layer coverage. Excess dye over monomolecular layer silver halide coverage can be used, but provides no advantage in the practice of the invention. It is preferredtoemploy dyes-at a concentration which will give monomolecular layer coverage, or nearly monolayer coverage, of the silver halide grains. Typical dye concentrations used to spectrally sensitize photographic emulsions for normal temperature exposures are about .02 to .08 gram dye per mole of silver. Such concentrations do not effectively increase sensitivity and contrast at temperatures of 180" C. and below. Combinations of dyes can also be used.

The invention can be practiced with any of the lightsensitive photographic silver halides, including silver bromide, silver bromoiodide, silver chlorideysilver chlorobromide, and silver chlorobromoiodide. Silver bromoiodide emulsions in which the halide is at least 90 mole percent bromide, are especially useful in the practice of the invention. The silver halide grains can be of any suitabletype, such as octahedral or cubic grain. Conventional negative, developing-out, unfogged silver halide emulsions are used in this invention. The silver halide emulsion may contain chemical sensitizers, antifoggants, stabilizers, speed increasing compounds, hardeners, plasticizers, and may utilize the binders described and referred to in Beavers US. Pat. 3,039,873 1962), col. 10-13. Advantageously, the silver halide is free from chemical foggants, such as stannous chloride.

The silver halide grains can be coated on any suitable support, such as cellulose acetate, paper or polyester such as poly(ethylene terephthalate) or other conventional photographic supports. If desired, the silver halide grains can be vacuum deposited on suitable supports to provide binderless silver halide coatings, which can be spectrally sensitized by bathing in a suitable solvent solution of the sensitizing dye.

The temperature at which the pre-exposure is made in the practice of the invention is from about '180 C. and below, such as down to the temperature of liquid helium, i.e.,. about -269 C. Liquid air (186 C.) or liquid nitrogen (--196 C.) can be conveniently used to lower the temperature of silver halide for the low temperature exposure.

In accordance with .the practice of the invention, the photographic element is warmed after the pre-exposing step to a temperature substantially above 180" C. The temperature, to which the element is warmed can be at least 25 C. and preferably is at least 0 C. up to 50" C. or higher. Highly satisfactory results are obtained when the emulsion is warmed up to ambient room temperatures, such as from about 20 to 25 C. a 1

, It should be noted that the processes of this invention can be conducted on a continuous basis by continually feeding a web of film carrying the dyed silver halide grains into a chamber cooled to the desired temperature and equipped to preexpose the film at the desired temperature, and continuously removing the film from the chamber. The temperature in the chamber can be regulated to below about 180 C. by introducing, for ex-' ample, liquid helium, liquid air or preferably liquid nitrogen. The chamber can be equipped with suitable seals which permit the continuous introduction and removal of film from the chamber.

The advantageous effects obtained in the practice of the invention are observed when exposures are conducted at atmospheric pressures or atreduced pressures, such as under high vacuum. The process of the invention is, therefore, adaptable for use in electron microscopes.

Emulsions which have been given low temperature exposures in accordance with the invention are advantageously processed under conventional conditions, i.e'., using standard developers and normal temperatures, such as above about 0 C. for example, up to about50 C., and preferably at about room temperature or about 20 to 25 C.

The following examples are included for a further understanding of the. invention. Except where otherwise noted, the emulsion exposures are made with a 1000 watt tungsten lamp operatedat a color temperature of 3000 K. The film is placed cm. from the light source during exposure, and all exposures are through a Dewar flask containing the emulsion. After processing, the exposure densities are read on a Macbeth desitometer through a red filter.

EXAMPLE 1 A gelatin silver iodobromide emulsion is prepared substantially as described in French Pat. 1,497,202 without chemical sensitization. The crystal habit of the silver halide grains in this preparation is cubic. The emulsion is coated on a cellulose acetate base with mg. Ag/sq. ft., 200 mg. gelatin/sq. ft., and 800 mg./mole Ag of 1,l'-diet-hyl- 2,2'-cyanine chloride.

(A) One strip of this photographic film is exposed for ten minutes through a step tablet while immersed in liquid nitrogen (196 C.), to a 1000 watt tungsten lamp filtered by a Wratten 16 filter (which limits exposure to wavelengths longer than 530 nm.'). The exposed film is then developed for 12 minutes at 20 C. in a solution comprising 2.5 g. N-methyl-p-aminophenol sulfate, 10.0 g. ascorbic acid, 35.0 g. sodium metaborate and 1.0 g. potassium bromide dissolved in suflicient water to make 1 liter'of solution. The film is then fixed for 3 minutes, washed and dried. Densities are read through a red filter on a densitometer. The characteristic curve obtained is shown as cuve 1 in FIG. 1. Curve 1 of FIG. 1 indicates the speed and contrast of low temperature exposure to non-blue light (wavelength longer than 530 nm.).

(B) Another strip of the photographic film described above is exposed for 1 /2 minutes while immersed in liquid nitrogen (-l96 C.) to a 1000 watt tungsten lamp filtered by one Wratten 36 filter, one Wratten 38A filter (this filter combination limiting the exposure to the 370 to 460 nm. spectral region) and a filter having a neutral density of 1.78 (to provide a low intensity overall latent image exposure). The film is then removed from the liquid nitrogen, allowed to warm to room temperature, reimmersed in the liquid nitrogen and exposed for 10 minutes through a step tablet and a Wratten l6 filter. The film is then developed, fixed, washed and dried as above. The characteristic curve obtained is shown as curve 2 in FIG. 1. The actual fog plus base density for this film is 0.18. Curve 2 of FIG. 1 indicates that an initial exposure of a low temperature dyed emulsion to blue light followed by warming to room temperature in accordance with this invention results in greatly increased speed and contrast characteristics for the emulsion.

(C) Another strip of the photographic film described above is exposed for 1 minute when immersed in liquid nitrogen (196 C.) to a 1000 watt tungsten lamp filtered by one Wratten 36 and one Wratten 38A filter. While the film is still immersed in the liquid nitrogen, it is exposed for 15 minutes to a 1000 watt tungsten lamp filtered by a Wratten 92 filter, thereby limiting the exposure to a wavelength greater than 620 nm. This film is then removed from the liquid nitrogen, allowed to warm to room tem perature, reimmersed in liquid nitrogen, and exposed for 10 minutes through a step tablet and a Wratten 16 filter. The film is then developed, fixed, washed and dried as above. The charactreistic curve obtained is shown as curve 3 in FIG. 1. The actual fog plus base density for this film is 0.06. Curve 3 of FIG. 1 indicates that low temperature blue light exposure followed by a Herschel exposure greatly increases the speed and contrast of the emulsion when image-exposed at low temperature.

(D) A fourth strip of the photographic film described above is exposed for two minutes through a step tablet, while immersed in liquid nitrogen (-196 C.), to a 1000 watt tungsten lamp filtered by one Wratten 36 and one Wratten 38A filter. The exposed film is then developed, fixed, washed and dried as above. Curve 4 of FIG. 1 (outside the present invention) shows the characteristic curve for low temperature imagewise blue light exposure of a dyed emulsion according to this example.

(E) A fifth strip of the photographic film described above is exposed for 1 minutes while immersed in liquid nitrogen (--196 C.), to a 1000 watt tungsten lamp filtered by one Wratten 36 filter, one Wratten 38A filter, and a filter having a neutral density of 1.78. The film is then removed from the liquid nitrogen, allowed to warm to room temperature, reimmersed in liquid nitrogen, and exposed for two minutes through a step tablet to a 1000 Watt tungsten lamp filtered by one Wratten 36 and one Wratten 38A filter. The exposed film is then developed, fixed, washed and dried as above. The characteristic curve obtained, shown as curve 5 in FIG. 1, demonstrates the increased speed and contrast shown by a dyed emulsion subjected to treatment according to a method of the invention.

EXAMPLE 2 (A) The photographic film described in Example 1 is used for all the exposures described in Example 2. A strip of this film is exposed for minutes, at room temperature, through a step tablet to the 1000 watt tungsten lamp filtered by a Wratten l6 filter. The emulsion is then developed, fixed, washed, and dried as in Example 1. The characteristic curve obtained, shown as curve 1 in FIG. 2, demonstrates the relatively poor speed and contrast shown by a dyed emulsion when treated accordinn to this example.

(B) Another strip of this photographic film is exposed for 1 /2 minutes, while immersed in liquid nitrogen (-196 C.), to a 1000 watt tungsten lamp filtered by one Wratten 36 filter, one Wratten 38A filter and a filter having a neutral density of 1.78. The film is then removed from the liquid nitrogen and allowed to warm to room temperature. This emulsion is then exposed for 10 minutes, at room temperature, through a step tablet to light filtered by a Wratten l6 filter. The film is then developed, fixed, washed and dried as in Example 1. The characteristic curve obtained, shown as curve 2 in FIG. 2, demonstrates the greatly increased speed and contrast of a dyed emulsion when treated according to a method of the invention.

(C) A third strip of this photographic film is exposed for 1 minute, while immersed in liquid nitrogen (-196 C.), to a 1000 watt tungsten lamp filtered by one Wratten 36 and one Wratten 38A filter. While the film is still immersed in the liquid nitrogen it is exposed for 24 minutes to the 1000 watt tungsten lamp filtered by a Wratten 92 filter. The film is then removed from the liquid nitrogen and is allowed to warm to room temperature. This emulsion is then exposed for 10 minutes, at room temperature, through a step tablet to light filtered by a Wratten 16 filter. The film is then developed, fixed, washed and dried as in Example 1. The characteristic curve obtained, shown as curve 3 in FIG. 2, demonstrates the increased emulsion speed and contrast obtained according to this method of the invention.

(D) A fourth strip of this photographic film is exposed for 2 minutes, at room temperature, through a step tablet to a 1000 watt tungsten lamp filtered by one Wratten 36 filter and one Wratten 38A filter. The exposed film is then developed, fixed, washed, and dried as in Example 1. The characteristic curve obtained, shown as curve 4 in FIG. 2, demonstrates the relatively poor speed and contrast shown by an emulsion subjected to room temperature blue light exposure with the low temperature pre-exposure of the invention.

(13) A fifth strip of this photographic film is exposed for 1 /2 minutes, while immersed in liquid nitrogen (-196" C.), to a 1000 watt tungsten lamp filtered by one Wratten 36 filter, one Wratten 38A filter and a filter having an neutral density of 1.78. The film is then removed from the liquid nitrogen and allowed to warm to room temperature. This emulsion is then exposed for 2 minutes, at room temperature through a step tablet to light filtered by a Wratten 36 filter and a Wratten 38A filter. The film is then developed, fixed, washed, and dried as in Example 1. The characteristic curve obtained, shown as curve 5 in FIG. 2, demonstrates the increased emulsion speed and contrast obtained according to this method of the invention.

EXAMPLE 3 A gelatin silver iodobromide emulsion is prepared substantially as described in French Pat. 1,497,202, without chemical sensitization or dye addition, and is coated on a cellulose acetate base. The crystal habit of the silver halide grains for this emulsion is cubic. Two strips of this film are bathed for 20 minutes at 21 C. in a l0- M aqueous solution of l,l'-diethyl 2,2'-cyanine chloride.

(A) The first strip of the bathed film is exposed for 5 minutes, while immersed in liquid nitrogen (-196 C.), through a step tablet to the 1000 watt tungsten lamp filtered by a Wratten 16 filter. The emulsion is then developed, fixed, washed, and dried as in Example 1. The characteristic curve obtained is shown as curve 1 in FIG. 3. This film is not given the low temperature preexposure of the invention.

(B) The second strip of this bathed film is exposed for 1 /2 minutes, while immersed in liquid nitrogen (196 C to a 1000 watt tungsten lamp filtered by one Wratten 36 filter, one Wratten 38A filter and a neutral density of 1.78. The film is then removed from the liquid nitrogen allowed to warm to room temperature, reimmersed in the liquid nitrogen and exposed for minutes through a step tablet and a Wratten l6 filter. The film is then developed, fixed, washed and dried as in Example 1. The characteristic curve obtained, shown as curve 2 in FIG. 3, demonstrates the increased speed shown by an emulsion treated pre-exposed at low temperature according to a method of the invention.

EXAMPLE 4 A gelatin silver iodobromide emulsion is prepared by a modification of the procedure described in French Pat. 1,497,202, without chemical sensitization or dye addition. This emulsion is coated on a cellulose acetate base. The crystal habit of the silver halide grains is octahedral. Two strips of this film are bathed for 20 minutes at 21 C. in a M aqueous solution of 1,1-diethyl 2,2-cyanine chloride.

(A) The first strip of the bathed film is exposed for 5 minutes, while immersed in liquid nitrogen (-196 C.), through a step wedge to the 1000 watt tungsten lamp filtered by a Wratten l6 filter. The emulsion is then developed, fixed, washed, and dried, as in Example 1. The characteristic curve obtained, shown as curve 3 in FIG. 3, demonstrates the relatively poor emulsion speed and contrast achieved by the method of the example, which lies outside the present invention (the low temperature pre-exposure being to radiation longer than 460 nm.).

(B) The second strip of this bathed film is exposed for 1 minutes, while immersed in liquid nitrogen (l96 C.), to the 1000 watt tungsten lamp filtered by one Wratten 36 filter, one Wratten 38A filter and a neutral density of 1.78. The film is then removed from the liquid nitrogen, allowed to warm to room temperature, reimmersed in the liquid nitrogen and exposed for 5 minutes throu h a step tablet and a Wratten 16 filter. The film is then developed, fixed, washed and dried as in Example 1. The characteristic curve obtained, shown as curve 4 in FIG. 3, depicts the greatly increased emulsion speed and contrast achieved by a method of the invention.

The invention has been described detail with particular reference to preferred embodiments thereof, but, it will be understood that variations and modifications can be eifected within the spirit and scope of the invention.

'1 claim:

1. A process for increasing the speed and contrast of photographic silver halide grains free from chemical foggants, said grains having adsorbed thereto a methine sensitizing dye, the highest occupied electronic energy level of said dye, in its unaggregated form at room temperature, being more positive than the highest occupied energy level in the valence band of the silver halide, and the lowest vacant electronic energy level of said dye, in its unaggregated form at room temperature, being more positive than the conduction band of the silver halide, said dye trapping electrons at a depth of not more than .7 ev. below the conduction band of the silver halide at temperatures below about l80 C., said silver halide having a sufiicient amount of said dye adsorbed thereto to effectively incerase the speed of said silver halide when exposed at a temperature below about 180 C., which comprises:

(1) cooling said silver halide grains to a temperature below about -180 C.;

(2) giving said silver halide grains a uniform, nonimagewise exposure to radiation having a wavelength of from about 370 to about 460 nm. while the temperature of said grains is maintained at less than about 180 C.; and

(3) warming said element to a temperature substantially above -1=80 C. prior to imagewise exposure.

2. A process for increasing the speed and contrast of photographic silver halide grains free from chemical foggants, said grains having adsorbed thereto to methine sensitizing dye, the highest occupied electronic energy level of said dye, in its unaggregated form at room temperature, being more positive than the highest occupied energy level in the balence band of the silver halide, and the lowest vacant electronic energy level of said dye, in its unaggregated form at room temperature, being more positive than the conduction band of the silver halide, said dye trapping electrons at a depth of not more than .7 ev. below the conduction band of the silver halide at temperatures below about 180 C., said dye having at least one of the following formulas:

wherein h, m, n and p each represents an integer of from 1 to 2; L represents a methine linkage; R R and R each represents a number selected from the group consisting of an alkyl group and an aryl group; R and R each represents an alkyl group containing from. 1 to 6 carbon atoms; X and X each represents an acid anion; and, Z Z and 2;, each represents the atoms necessary to complete a 5- to 6-membered heterocyclic nucleus of the type used in methine dyes; said silver halide having a sufiicient amount of said dye adsorbed thereto to effectively increase the speed and contrast of said silver halide when exposed at a temperature above about 1-80 C., which compirses:

(1) cooling said silver halide grains to a temperature below about l C.;

(2) giving said silver halide grains a uniform, nonimagewise exposure to radiation having a wavelength of from about 370 to about 460 nm. while the temperature of said grains is maintained at less than about l80 C.; and

(3) warming said element to a temperature substantially above -l80 C. prior to imagewise exposure.

3. The process as defined in claim 2 wherein said Z Z and Z in the structural formulas each represents the atoms required to complete a nucleus selected from the group consisting of a thiazole nucleus, an oxazole nucleus, a selenazole nucleus, and a quinoline nucleus.

4. The process as defined in claim 3 wherein said dye is adsorbed onto said silver halide in a concentration suflicient to give monomolecular layer coverage of the silver halide grains.

5. A photographic process for increasing the speed and contrast in the region of spectral sensitization of a lightsensitive photographic silver halide emulsion, said emulsion comprising silver halide grains having adsorbed thereto a methine sensitizing dye, said dye selected from the group consisting of 1,1',3,3',-tetramethyl-2,2'-cyanine dye salt; a 3,3'-diethy1thiacarbocyanine dye salt; Z-(p-dimethylaminostyryl)-1-methyl pyridinium dye salt; 1,1-diethyl- 2,2'-cyanine dye salt; 1,l'-dimethyl-2,2'-cyanine dye salt; l,l'-diethyl-2,4-cyanine dye salt; and, 1-methyl-1',9-diethyl-2,2'-cya nine dye salt; said silver halide having a suflicient amount of said dye adsorbed thereto to effectively increase the speed and contrast of said silver halide when exposed at a temperature of about C., which comprises:

(1) cooling said silver halide grains to a temperature below about --180 C.;

(2) giving said silver halide grains a uniform, nonimagewise exposure to radiation having a wavelength of from about 370 to about 460 nm. while the temperature of said grains is maintained at less than about --180 C.; and

(3) warming said element to about 0 to 50 C. prior to imagewise exposure.

6. A photographic process for increasing the speed and contrast in the region of spectral sensitivity of a lightsensitive photographic silver halide emulsion, said emulsion comprising an unfogged cubic regular-grain silver bromoiodide gelatin emulsion, the grains of said emulsion having a size of about 0.2 micron, said grains having absorbed thereto a monomolecular layer coverage of 1,1- diethyl-2,2-cyanine dye salt, which comprises:

(1) cooling the photographic silver halide emulsion to a temperature below about 180 C.;

(2) uniformly exposing the emulsion to radiation of a wavelength of from about 370 to about 460 nm. through a neutral density filter to produce a fog density up to about 0.2; and

(3) warming the exposed emulsion to about 20 C.

prior to imagewise exposure.

7. A photographic process for increasing the speed and contrast in the region of spectral sensitization of a light-sensitive photographic silver halide emulsion, the silver halide grains of said emulsion having adsorbed thereto a methine sensitizing dye, the highest occupied energy level of said dye, in its unaggregated form at room temperature, being more positive than the highest occupied energy level in the valence band of the silver halide, and the lowest vacant electronic energy level of said dye, in its unaggregated form at room temperature, being more positive than the conduction band of the silver halide, said dye trapping electrons at a depth of not more than .7 ev. below the conduction band of the silver halide at temperatures below about l80 C.; said silver halide having a sufiicient amount of said dye adsorbed thereto to efiiective- 1y increase the speed and contrast of said silver halide when exposed at a temperature above about l80 C., which comprises:

(1) cooling the photographic silver halide emulsion to a temperature below about -l80 C.;

(2) uniformly exposing the emulsion to radiation of a wavelength of from about 370 to about 460 nm. for suflicient time to produce a latent image having a density at least about 70% of the maximum developable density;

( 3) uniformly exposing the emulsion to a Herschel exposure of a wavelength greater than about 620 nm., said Herschel exposure having an intensity sufficient to substantially destroy said latent image; and

(4) warming the emulsion to a temperature substantially about --180 C. prior to imagewise exposure.

8. A photographic process for increasing the speed and contrast of a light-sensitive photographic silver halide emulsion, the silver halide grains of said emulsion having adsorbed thereto a methine sensitizing dye, the highest occupied electronic energy level of said dye, in its unaggregated form at room temperature, being more positive than the highest occupied energy level in the valence band of the silver halide, and the lowest vacant electronic energy level of said dye, in its unaggregated form at room temperature, being more positive than the conduction band of the silver halide, said dye trapping electrons at a depth of not more than .7 ev. below the conduction band of the silver halide at temperatures below about 180 C.; said dye having at least one of the following formulas:

wherein h, m, n, and p each represents an integer of from 1 to 2; L represents a methine linkage; R R and R each represents a member selected from the group consisting of an alkyl group and an aryl group; R and R each represents an alkyl group containing from 1 to 6 carbon atoms; X and X each represents an acid anion; and Z and Z and Z each represents the atoms necessary to complete a 5- to 6-membered heterocycllic nucleus of the type used in methine dyes; said silver halide having a sufiicient amount of said dye adsorbed thereto to efiectively increase the speed and contrast of said silver halide when exposed at a temperature above about -l C., which comprises:

(1) cooling the photographic silver halide emulsion to a temperature below about l80 C.;

(2) uniformly exposing the emulsion to light of a wavelength of from about 370 to about 460 nm. for sufficient time to produce a latent image having a density at least about 70% of the maximum exposure density;

(3) maintaining the emulsion at the temperature below about '180 C. and uniformly exposing the emulsion to a Herschel exposure of a wavelength greater than about 620 nm., said Herschel exposure being of an intensity sufiicient to substantially destroy said latent image; and

(4) warming the emulsion to a temperature substantially above -l80 C. prior to imagewise exposure.

9. The process as defined in claim 8 wherein said dye is adsorbed onto said silver halide in a concentration suflicient to give monomolecular layer coverage of the silver halide grains.

10. The process as defined in claim 8 wherein said Z Z and Z in the structural formulas each represents the atoms required to complete a nucleus selected from the group consisting of a thiazole nucleus, an oxazole nucleus, a selanazole nucleus, and a quinoline nucleus.

11. A photographic process for increasing the speed and contrast in the region of spectral sensitization of a light-sensitive photographic silver halide emulsion to be exposed at temperatures above about C., the silver halide grains of said emulsion having adsorbed thereto a methine sensitizing dye selected from the group consisting of l,l',3,3'-tetramethyl-2,2'-cyanine dye salt; a 3,3- diethylthiacarbocyanine dye salt; 2-(p-dimethylaminostyryl) l methyl pyridinium dye salt; l,l'-diethyl-2,2-cyanine dye salt; l,l-dimethyl-2,2-cyanine dye salt; l,l'- diethyl-2,4-cyanine dye salt; and, l-methyl-l',9-diethyl- 2,2-cyanine dye salt; said silver halide having a suflicient amount of said dye adsorbed thereto to elfectively increase the speed and contrast of said silver halide when exposed at a temperature of about -l80 C., which comprises:

(1) cooling the photographic silver halide emulsion to a temperature below about -180 C.;

(2) uniformly exposing the emulsion to light of a wavelength of from about 370 to about 460 nm. for sufficient time to produce a latent image having a density at least about 70% of the maximum density;

(3) maintaining the emulsion at the temperature below about -180 C. and uniformly exposing the emulsion to a Herschel exposure of a wavelength greater than about 620 nm., said Herschel exposure being of an intensity sufiicient to substantially destroy said latent image; and

(4) warming the emulsion to between about 0 C. to

50 C. prior to imagewise exposure.

12. The process as defined in claim 11 wherein said dye is adsorbed onto said silver halide in a concentration sufficient to give monomolecular layer coverage of the silver halide grains.

13. A photographic process for increasing the speed and contrast in the region of spectral sensitization of a silver halide photographic emulsion to be exposed at temperatures above 180 C., said emulsion comprising an unfogged cubic-regular grain silver bromoiodide gelatin emulsion, the grains of said emulsion having a size of about 0.2 micron, said grains having adsorbed thereto a monomolecular layer coverage of a 1,1'-diethyl-2,2'-cyanine dye salt, which comprises:

(1) cooling the photographic silver halide emulsion to a temperature below about 180 C.;

(2) uniformly exposing the emulsion to light of a wavelength of from about 370 to about 460 nm. for suffi cient time to produce a latent image having a density at least about 70% of exposure density;

( 3) maintaining the emulsion at the temperature below about 180 C. and uniformly exposing the emulsion to a Herschel exposure of a wavelength greater than about 620 nm., said Herschel exposure being of an intensity suificient to substantially destroy said latent image; and

(4) warming the emulsion to about 20 C. prior to ima-gewise exposure.

14. Photographic silver halide grains obtained by the process of claim 1.

15. Photographic silver halide grains obtained by the process of claim 2.

16. A photographic silver halide emulsion obtained by the process of claim 6.

17. A photographic silver halide emulsion obtained by the process of claim 7.

18. A photographic silver halide emulsion obtained by the process of claim 8.

19. A photographic silver halide emulsion obtained by the process of claim 13.

References Cited Blair: A Note on Photographic Sensitivity Effect is JOSA', vol. 24, pp. 135-156, June 1934.

James e't in Photographic Science & Engineering, vol.. 4, No. 4 (1263). NORMAN G. TORCHIN, Primary Examiner R. E. FICHDER, Assistant Examiner US. Cl. X.R.

wy UNITED S ATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2i38l ,O77\ Dated August 1 97 Inventor(5) Lillian M. Kellogg It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

C olumn 3, line L L "temperature" should. read. temperatures Column 3, line 71 "Verlagsgell should. read. Verl'agsgesell- Column L line 20, "-OR:" should. read. -CH= Column 5', line 27, "Anhyldro-l 'ethyl3-6-sulfoethylthia-2'- Oyanine" should. read. Anhydro-l 'ethyl-3-Q-sulfoethylthia-Z'- oyanlne Column 6, line EL "desitometer" should. read. densitometer Column 7, line 'I "Cuve" should. read curve Column 9, line 59, "inoerase" should. read. increase Column 1 0, line 3, balence" should. read. valence Column l 0, line 'IL "X (9 should. read. X Q Column 1 0, line 22, "number", should. read. member Column 11 line 7, "absorbed", should. read. adsorbed.

Column l2, line 33, "selanazole" should. read. selenazole Signed and sealed this 20th day of February 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attestlng Officer Commissioner of Patents 

